[G6Tanuki]

The matching is 'good enough' with pretty much any 1:1 audio transformer. It assumes that the average DC current through the PA is something close to the average DC in the 6BW6 audio-output stage - get around 45mA flowing in them both and the matching is good-enough, and the magnetic fields from the static DC component balance-out in the transformer same as they would in a push-pull audio amp.

Remember we're not talking hi-fi here!

In times-past I did something very similar with a transmitter using an AUY10 as the RF amp and a NKT404 as the audio amp.

Coupled together using a 12-0-12V winding on a little power-transformer, with a neon across the 240V primary to indicate modulation. Yes - Germanium PA stage and class-A modulator! Both nice TO3 cased transistors, whole thing put out about 10W for 3A current draw from a 12V battery. [will remain quiet about the frequency...]